The present invention relates to machine tools. In particular, the present invention is an improved system for holding work pieces which combines an air cushion support of the work piece, and a vacuum hold down of the work piece.
In the past, some machine tools have been provided with air support structures in which a work piece is effectively floated on an air cushion over a work table. This permits easy movement of the work piece by the operator, and is particularly advantageous when a number of operations will be performed at different locations on the work piece. The air floatation systems, however, have the disadvantage that inaccuracies can result due to inadvertant movement of the work piece and work piece support with respect to the machine tool. An example of a prior art system having an air support is shown in U.S. Pat. No. 3,782,847.
Other prior art systems have been provided with various types of vacuum hold downs or vacuum chucks for holding a work piece securely in position while work is being performed. Examples of these prior art systems include U.S. Pat. Nos. 2,782,574; 3,233,887; and 3,790,153.